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S t u d y G u i d e a n d Wo r k s h e e t s
LOGICAL FALLACIES
Blair Mahoney • mahoneyb@mhs.vic.edu.au • Melbourne High School
H
Y
Fallacies of Relevance
This group of fallacies rely on an appeal to evidence which is irrelevant or does not logically support the conclusion or
point at issue. At times the premises may seem to be relevant to the conclusion but in fact are not and therefore cannot
possibly establish its truth.
1.
ATTACKING THE PERSON (Ad Hominem)
An argument in which the attack shifts from the point at issue to the character of the opponent is fallacious when the
character of the opponent is not relevant to the point at issue.
These generally occur in one of the following two forms.
(a) Abusive Ad Hominem (or Poisoning the Well)
Here the attack is a direct attack on the character of the opponent and occurs before the opponent has had the chance to
give their argument. It attempts to put the opponent in a position from which they are unable to reply usually by questioning their honesty and integrity, thus seeking to defame or discredit them.
Example:
Do not bother going to Mr Paul 's lesson. He is a boring boffin with little idea of the truth.
Example:
You claim that John Howard is a great Prime Minister, but you are an ignorant fool.
(b) Circumstantial Ad Hominem (Genetic Fallacy)
This occurs where a speaker produces reasons why his opponent would be expected to hold a certain point of view
rather than arguing the case put forward. Here the attack is indirect suggesting that they hold their views chiefly because
of their special circumstances or interests.
Example:
Of course you would say that the Liberal Party should be in power, your parents have always voted liberal
haven 't they.
Example:
We can 't believe what Coldberg says about pork being unclean. After all he is a Jew and he's not allowed
to eat pork.
2.
YOU TOO FALLACY (Tu Quoque)
In this fallacy appeal is made to the hypocrisy of the opponent for saying one thing and for doing something different.
This happens when in trying to show that THEY are not at fault, a speaker points out that their opponent is as bad as
they are.
Example:
Look who 's telling me to stop smoking ? You smoke more than I do.
B l a i r M a h o n e y!
Melbourne High School
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Example:
What do you mean that I should drive with my seat belt on? I have seen you drive over the speed limit
often enough.
3.
APPEAL TO WRONG AUTHORITY (Ad Verecundiam)
When a person appeals to the opinion of some respected, well-known or influential person/group to support their position they are said to be appealing to authority.
In this fallacy an appeal is made to the authority of a person and the sphere of influence/authority of their supporter is
outside the point of issue then such an appeal is fallacious.
Example:
Cars from Tiger Bill 's are the best because Shane Warne the Australian cricketer says so.
Example:
You must recognise the value of cooking with herbs; Mahatma Gandhi always used herbs in his food.
4.
APPEAL TO PITY (Ad Misericordiam)
This fallacy is committed when pity ( or similar sentiment) is appealed to for the sake of getting a conclusion accepted,
where that conclusion is concerned more correctly with a matter of fact.
Example:
This assignment deserves a better mark, after all both my parents were away when it was due and I had to
look after myself.
Example:
Because my client has had a hard life, rejected by his parents and left school early you must recognise that
he should not be found guilty of the theft he is accused of.
5.
APPEAL TO POPULAR OPINION (Ad Populum)
When the evidence provided to support a proposal involves the appeal to widely-held beliefs, common prejudices or the
views of a popular group or ideology it is often the case that such an appeal is fallacious.
Just because "everyone believes x" does not imply or mean that "x is true". Often the everybody referred to are of a specific and attractive kind. Also, just as popular attractive images or phrases are associated with x does it necessarily follow
that x is right?
A popular version of this fallacy is claiming that something is right because it has ALWAYS been done.
Example:
You should get a drivers’ license because everyone does.
B l a i r M a h o n e y!
Melbourne High School
2
Example:
You should vote Labor, all the 'with it' people do.
6.
APPEAL TO FORCE (Ad Baculum)
This fallacy occurs when an appeal is made to force, threat, or to undesirable consequences in order to coerce acceptance
of a conclusion. It is argued that a certain viewpoint is correct because otherwise some deliberate harm will be done to
the other person.
Example:
My son deserves the job because if he doesn't get it, his big brothers will call on you.
Example:
Before rejecting my opinion son, you should remind yourself of who it is who houses you, feeds you and
pays your University fees.
7.
APPEAL TO IGNORANCE (Ad Ignorantiam)
When there is an expectation to prove the conclusion, an appeal to the inability of an opponent to disprove your conclusion is fallacious. The general situation is that someone argues that because you cannot prove that something is false,
that it must be true.
Example:
There must be intelligent life in outer space, for no-one has been able to prove that there isn't.
Example:
Ghosts exist, after all no one has ever been able to prove that they do not.
8.
APPEAL TO NATURE
This argument goes that because something is natural, it must be better.
Example:
Do not immunise your baby against diseases like polio and diptheria. Nature has its own wonderful protection. Its called natural immunity. This is the right way, the natural way.
9.
APPEAL TO ASSOCIATION
This fallacy occurs when a person condemns or approves something or a person because of what it is associated with.
Example:
I agree with apartheid. The indigenous people of Africa are violent and do not deserve a vote.
B l a i r M a h o n e y!
Melbourne High School
3
10.
ILLICIT APPEAL TO FEELINGS
This occurs when an appeal to emotions is made, and it is irrelevant.
Example:
Your opinion of her is unkind, so it must be wrong.
11.
ARGUMENT BY TRANSFERENCE
This is when someone transfers what they feel about something, or themselves, to another object or person.
Example:
This subject is boring. I don’t understand it.
12.
APPEAL TO RELATIVITY
This occurs when something is compared to another situation when the comparison is irrelevant.
Example:
You claim that our police force is corrupt. You should see what the police are like in India!!!
13.
FALLACY OF STEREOTYPING
This fallacy occurs when an argument is put forward about a person or group which is not typical of that stereotyped
class of objects.
Example:
I am lunching with a professor I have not met before. I won't hurry because he will probably be vague and
not turn up on time anyway.
Example:
I'm not going to that lecture on Environmental Issues. The lecturer is a hippy and we know where they
stand on those sort of issues.
14.
NON SEQUITUR (IT DOES NOT FOLLOW)
Any argument where the conclusion does not follow from the premises is a non sequitur.
Example:
You should play more sport so that your school results will improve.
B l a i r M a h o n e y!
Melbourne High School
4
WORKSHEET 1: FALLACIES OF RELEVANCE
The fallacies below are fallacies of Relevance. Identify the particular type of fallacy and explain how the argument in
question involves that fallacy.
1. We must reject Stevenson's claim that abortion is wrong. After all being a Catholic he is bound to believe this narrowminded and religious viewpoint.
2. We should take no notice of what Jones says about the environment. He's got long hair, no shoes and obviously hasn't
done a day's work in his life.
3. We can ignore what Karl Marx said about Capitalism. After all, he was so hopeless he didn't even support his own
family.
4. Professor Smith, who received the Nobel prize for Economics, said that you should drink XXXX.
5. Humans have always solved their disputes by war, so battle must be the best way.
6. New, improved and desired by all the best people, you too should join the rush to smoke "Wheezers"
7. If you do not convict this murderer one of you may be her next victim.
8. These factory workers do not need a Union and any one who thinks otherwise need not bother coming back to work
tomorrow.
9. Since no-one has ever shown conclusively that smoking marijuana is bad for you, we can safely conclude that it is a
safe practice.
10. It is true that several University professors have claimed that marijuana is harmless and non-addictive, but these
same people have admitted to taking the drug. So we should certainly disregard their views.
11. What do you mean I cannot cure cancer with my fruit diets ? Anyway it is up to you to prove that I cannot.
12. I never go to that nightclub. It is frequented by bikies.
13. We do not believe in blood transfusions. It is not natural to accept blood from another person.
14. The majority of people do not trust politicians so politicians cannot be trusted.
15. Tom's claim that infidelity is wrong must be rejected. After all he has been married three times.
16. Under age drinking is OK. Everyone my age is doing it.
17. I deserve a wage rise as I have a sick wife, an invalid mother and five kids to support.
18. I would not take any notice of Tom's warnings against alcoholism - he's quite fond of a drink himself.
19. Whenever people are young, alive and happy you will find people drinking Swillo.
20. Nobody has been able to prove that there is life after death, so we can be sure that there is no such thing.
B l a i r M a h o n e y!
Melbourne High School
5
Fallacies of Presumption
These fallacies occur when a mistaken argument/statement arises from reliance upon some proposition that is assumed
to be true, but it is in fact false, or dubious, or without support. The proponent's argument is thereby flawed. The importance of understanding such assumptions is the need to sort out several hidden assumptions before rational reply can
begin.
1.
SLIPPERY SLOPE
This fallacy occurs when an argument involves an appeal to a "chain of events" which are claimed to lead from acceptance of an opponent's proposal to some undesirable consequence. This happens when it is reasoned that because Action
A MAY lead to Action B and so on to Action Z, which is a most undesirable action that we should threat Action A as if it
were action Z already.
Example:
Teenage parties sometimes deteriorate all the way down and become uncontrolled promiscuity; so on no
account will my teenager be allowed to go to a party no matter what the circumstances
Example:
If we let boat people stay in Australia, then we'll have to accept anyone who sneaks into this country and
then we'll have to accept everyone who wants to come here which will lead to over population and starvation in Australia. Thus we can't let boat people stay.
2.
BEGGING THE QUESTION/CIRCULAR ARGUMENT (Petitio Principii)
This fallacy occurs when an arguer assumes to be true what they are actually seeking to prove is true. It occurs when
somehow the conclusion has already been assumed in the premises. In general this fallacy refers to the attempt by the
proponent to avoid giving reasons or evidence at all.
Example:
I know that God exists because the Bible says so and I know that the Bible says the truth because it is the
word of God
Example:
Since the exercise of unrestricted freedom is dangerous it follows that it is harmful to allow people unfettered liberty.
3.
COMPLEX QUESTION
This fallacy occurs when a question is asked in such a way as to presuppose the truth of some assumption buried in that
question. These can occur in the following two forms:
B l a i r M a h o n e y!
Melbourne High School
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A)
Loaded Question
Here the wording of the question limits the responder to an answer of 'Yes' or 'No' hence admitting to or denying
the assumption in the question.
Example:
Have you stopped beating up your wife these days?
Example:
No-one in their right minds would accept the ludicrous and childish views ofmy opponent, would they ?
B)
Limited Alternatives
Here the nature of the question is such that the response of the person provides them with only a limited choice in
the way they can respond
Example:
If you are not going to be a good boy then Santa will not bring you any presents.
Example:
Are you going to be intelligent and agree with me or persist in being stupid and disagree with me?
3.
FALSE CAUSE (Post Hoc Ergo Propter Hoc)
This fallacy occurs when one treats as the cause of a thing what is not really the cause of that thing, or more generally,
when one blunders in reasoning that is based upon two events affecting each other. It is often seen when it is assumed
that just because A precedes B then A must definitely have caused B.
Example:
Inflation started to soar right after the Labor Party came into power. Obviously, they are responsible for
Australia 's inflation.
Example:
Whatever you do, do not invite Paul to your party. I've been to three parties where he was there and they
were all boring.
4.
STRAW MAN FALLACY
This fallacy occurs when someone misrepresents an opponent's argument and thus attacks the wrong issue.
Example:
"I think that students should be held responsible for the behaviour of other students in class."
"That won 't work, the teachers would be furious if you take away their authority."
B l a i r M a h o n e y!
Melbourne High School
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5.
BLACK AND WHITE THINKING
This is a form of straw man fallacy, and is committed by someone who deliberately assumes an exaggerated position for
his protagonist.
Example:
“This set book is too difficult for Year 11.”
“I suppose that you think they should read something like Dr Seuss.”
6.
BALD-HAIRY FALLACY
This fallacy involves the assumption that because there is a vague borderline between two things, that there is in fact no
difference between them. How many hairs must a man have on his head to be not bald? Just because it is impossible to
say how many there must be, does not mean that there is no difference between a bald person and a non-bald person.
Example:
Where does genius stop and madness begin ? Who can say ? Really all geniuses are mad.
7.
ACCIDENT
This fallacy occurs when one applies a generalisation to an individual case that it does not properly govern. This occurs
in two different ways;
A)
When it is assumed what is correct in normal circumstances remains correct in an abnormal situation.
B)
When it is assumed that what was acceptable in unusual circumstances remains so when normal circumstances
apply.
Example:
I'm sorry that you are dying of snakebite in the back seat but I can't go any faster because I'm in a 60 kilometres per hour zone.
Example:
Why do we have to go to school every day? During the Great Depression students were allowed to leave
school really young.
B l a i r M a h o n e y!
Melbourne High School
8
WORKSHEET 2: FALLACIES OF PRESUMPTION
The fallacies below are fallacies of presumption. Identify the particular type of fallacy and explain how the argument in
question involves that fallacy.
1.
I know that she loves me because she told me so and I can believe what she told me because she loves me.
2.
"People cannot help what they do." "Why not?" "Because they always follow the strongest motive." "But what is
the strongest motive?" "Why, the one that people follow, of course."
3.
Did the government make a botch of the Budget through plain stupidity or deliberate dishonesty?
4.
In a certain village it was noticed that sober and industrious farmers had at least one cow while those who had
none were lazy and drunken, so the local government official proposed that the farmers who had no cows be
given one, in order to make them sober and industrious.
5.
Since we know that exercise is good for people, we should encourage patients in recovery wards to jog, swim and
play sport.
6.
Free trade will be good for this country. The reason is obvious. Isn't it clear that unrestricted commercial relations
will bestow on all sections of this nation the benefits which result when there is an unimpeded flow of goods between countries?
7.
So you don't think that the marginal tax rate should be 50c in the dollar. I suppose you think it should be nothing.
8.
"I really think that Politicians are responsible for putting forward the case for and against the Republic." "I do not
agree with that because politicians only respond to issues of concern shown by the general population."
9.
Everyone has the right to their own property. Thus Jones, even though he's been declared insane, shouldn't have
had his gun taken from him.
10.
"This novel is too hard for Year 12." "I suppose you think that they should be reading comics."
11.
Gun control laws are wrong because they violate the citizen's right to bear arms.
12.
We should never give security clearances to homosexuals because they can be blackmailed into revealing classified secret information. They are subject to blackmail because we will revoke their security clearances if we find
out they are gay.
13.
Suicide is wrong. Just because people may be lonely or in debt or find life difficult is no excuse. Many people find
life difficult at times but do go to counsellors for help. So if you find a friend in trouble ensure they see a counsellor. That should prevent them from suiciding.
14.
"The driving age in Australia should be lowered to sixteen." "I do not agree as you are not mature enough to drink
until you are 18 !"
15.
"Economic rationalism is good for the country." "So you must be a capitalist ?"
16.
Whatever you do, do not walk under a ladder on Friday the 13th. I did and not long after I was off work for a
week.
17.
"The figures seem to indicate that your sales increased as a result of these misleading advertisements. Is that correct?" "No it is not." "So you admit then that your advertising was misleading. How long have you been engaging
in practices like these?”
B l a i r M a h o n e y!
Melbourne High School
9
Fallacies of Scope
These fallacies involve a failure to see the limitations or exceptions to an argument through the misuse of statistical information or through deliberate/unintentional use of information.
1.
HASTY GENERALISATION
This fallacy arises when a generalisation is drawn from a sample of the population but the size of the sample is too small
to support the size/scope of the generalisation.
Example:
That is the third time I've tried to ring Tom and the phone was engaged. He is always on the phone.
Example:
I had a terrible time with my former wife. I am never going to marry again because I have learned that no
women are easy to live with.
2.
COMPOSITION
This fallacy occurs when a claim that what is true about each element or member of a group will therefore be true about
the group as a whole.
Example:
All the members of the association were professionals so it must be a professional association.
Example:
My little brother can tear each of the pages in the telephone book in two. Therefore he can tear the telephone book in two.
3.
DIVISION
This fallacy involves a claim that what is true about a collection or group as a whole is necessarily true about each element of the group.
Example:
Morgan has a very expensive collection of paintings therefore each of his paintings must be expensive.
Example:
Our school has always won the interschool swimming carnival therefore all our students are champion
swimmers.
B l a i r M a h o n e y!
Melbourne High School
10
4.
BIASED SAMPLING
This fallacy occurs when a conclusion is reached about a group on the basis of a survey which is unrepresentative of the
population.
Example:
The last fifty people 1 spoke to at the Races all agree that Horse racing should be retained. Obviously this
is the majority view in Queensland.
Example:
I spoke to a number of people at the Soccer game recently and they all agree that Soccer is better than Australian Rules.
5.
FALLACY OF CENTRAL TENDENCY
This fallacy occurs when someone argues from an average characteristic to an individual characteristic or vice versa.
Example:
The average mark in that class is very high. All the kids in that class must be good at Logic.
Example:
The average size class in the school is 25. Hence the Logic class must have 25 students.
6.
MONTE CARLO FALLACY (GAMBLER'S FALLACY)
This fallacy occurs when a person treats an independent event as if it were a dependent event.
Example:
The number 8 has not come up all night on the roulette wheel. I'll bet on its coming up next, as it must
come up soon.
7.
MISUSE OF THE LAW OF AVERAGES
This occurs when someone treats a dependent event as if it were an independent event, that is, when mathematics is
applied to events that are not mathematical.
Example:
My father has never had an accident and he’s been driving for ages. He must be due to have one soon.
8.
FAULTY ANALOGY
This fallacy occurs when, using analogy, one finds that the differences between the events outweigh the similarities. It
can also occur when there is an important fundamental difference between the two linked qualities.
B l a i r M a h o n e y!
Melbourne High School
11
Example:
Young children are like young animals... rash and silly, so they should be taught instant obedience like
young dogs and horses.
Example:
Marriage is like a basketball game. Basketballers regularly take time outs to reflect on the state of the game
and thus couples should take time out from being with each other too.
9.
SLOTHFUL INDUCTION (Scapegoat Argument)
This fallacy occurs when a person blames someone else who is not to blame - usually because they are at fault themselves.
Example:
I just ran into a traffic sign. What stupid person would put a traffic sign there?
Example:
All the teachers fail my work because they hate me.
10.
FORGETFUL INDUCTION
This occurs when important and relevant information is overlooked.
Example:
Everyone should get social welfare. It’s not fair that some people are helped more than others.
B l a i r M a h o n e y!
Melbourne High School
12
WORKSHEET 3: FALLACIES OF SCOPE
The fallacies below are fallacies of Scope. Identify the particular type of fallacy and explain how the argument/statement
involves that fallacy.
1.
My father has never had an accident and he has been driving for years. He must be due to have an accident soon.
2.
I can't wait to get our Great Dane puppy. I know I will love it. I have loved the last few dogs we have had. They
were poodles and they were so easy to brush and wash.
3.
It must be my turn for a good hand of cards because I haven't had a decent hand all night.
4.
As saving is good for the individual, it must be good for the nation as a whole
5.
The school's orchestra is the best in the state so the sax player must be the best in the state.
6.
I should never have failed the driving test. The examiner was out to fail me.
7.
All the players were zone representatives so the team must have been a champion team.
8.
I spoke to a number of people at the Basketball and they all agreed that basketball was better than Australian
Rules.
9.
This is the first time there has been trouble after the school social so we should cancel all school socials because
there will be trouble.
10.
The average age of students at this school is 15. So the average age of students in year 12 at this school is 15 years.
11.
All the unemployed are dole bludgers. Only yesterday another one was charged with defrauding the Department
of Social Security.
12.
You can't be going to that demonstration. Only people who are communist would challenge the government policy on conscription.
13.
If person uses an axe continually it will be blunted. So it follows that, as the mind is a delicate instrument, if I use
it too much, I will dull it.
14.
Suzie lives in a large residential college so she must have a large room.
15.
I spoke to all the Seniors in the Logic class and they all agreed that I should take Logic in Year 11.
16.
Our school has won the interschool athletes competition for the last 25 years so all the champion athletes in the
region must have come to this school.
17.
The red has not come up on the Roulette wheel for the last five times so Red should come up next time.
18.
Professional boxers are like racehorses. Both compete in physical contests where money is involved. When a
racehorse is past its prime we simply put it out to pasture and forget about it. It seems reasonable to treat professional boxers in the same way.
19.
That student is a computer freak. You hardly see him during the day. He must have no friends.
20.
It was not my fault that the window broke. We were playing football in the yard and Tom kicked the ball too far.
B l a i r M a h o n e y!
Melbourne High School
13
WORKSHEET 4: FALLACIES- GENERAL
The fallacies below contain a range of general types. Identify the fallacy and explain how the statement/argument involves that fallacy.
1.
Logic is really easy. I know because Stephen told me and he knows all about it because he has already repeated
Senior twice and he knows all about Senior courses.
2.
The American Indians accuse the American Government of being unjust to them. We can dismiss this by remembering how the Indians treated the first white settlers.
3.
You cannot believe what Professor Threadbare says about the importance of higher salaries for teachers. As a
teacher himself he would naturally be in favour of more pay.
4.
If there were no private schools then the government would be free to regiment our children and indoctrinate
them with its atheistic ideas.
5.
It's impossible to donate to every charity that comes knocking at the door. There are literally hundreds of them. So
I do not give to any.
6.
No Mathematician has been able to demonstrate the truth of the famous last theorem of Fermat, so it must be
false.
7.
The accused is but a misguided youngster. He has admitted killing his parents but we should not judge him too
harshly as he stands here now alone and an orphan.
8.
Old Man Brown claims he saw a flying saucer land. But this can't be right. Brown cannot read or write and hasn't
got a clue what the experts have to say about it.
9.
Professor Spaulding's new theory must be true because all the reputable scientists agree with it. Of course I know
which scientists are reputable; they're the ones who keep up with all the new developments and research. Anyone
who keeps ahead of all the new developments will recognise the truth of a new theory like that of Professor
Spaulding.
10.
Was it through dishonesty or stupidity that the administration has hopelessly botched its foreign policy?
11.
I saw a dead possum climbing up a tree.
12.
America is a very rich country so all Americans are rich.
13.
If you don't help with the stocktake then don't bother coming back to work tomorrow.
14.
Con Job must be a good movie because it's been number one on the box office list for over three weeks now.
15.
I can't see any merit in Bob's argument in favour of stricter gun laws. After all, he owns a gun himself.
16.
I cancelled my flight with Rainbow Airways when I found out they have not had a crash for twelve years now.
They are due for one soon.
17.
Sally is only opposed to uranium mining because she is a conservationist.
B l a i r M a h o n e y!
Melbourne High School
14